Rust 'B' Gone

Cannot be auctioned, traded, bazaared, or delivered.
Cannot be obtained as a random reward from the Gobbie Mystery Box Special Dial and similar sources.

Each of the Item-slot items dropped by the Avatars which are used in the Mama Mia quest were a Key Item from one of the first seven Final Fantasy games. Rust 'B' Gone (called Rust-Rid in the original English translation) was a key item in Final Fantasy VI, which was used to remove the rust from a door in the city of Zozo in order for the party to gain access to Mount Zozo. One of the inhabitants of Zozo had the item.